This invention relates to a method of preparing a graphite fluoride by heterogeneous contact reaction between solid carbon and fluorine gas and an apparatus for performing this method.
Graphite fluorides are generally expressed by (CF.sub.x).sub.n, and (CF).sub.n and (C.sub.2 F).sub.n are typical examples of graphite fluorides already confirmed to exist as stable solid compounds. These graphite fluorides have been put into industrial use as lubricants, activating agents for electrolytic cells, water- and oil-repellents and anti-contamination agents for example, but there is an eager demand for an improved method for mass production of such graphite fluorides.
At present it is prevailing to prepare a graphite fluoride by heterogeneous contact reaction between carbon and fluorine gas as exemplified by the following equations: EQU 2nC(s)+nF.sub.2 (g).fwdarw.2(CF).sub.n (s) . . . (1) EQU 4nC(s)+nF.sub.2 (g).fwdarw.2(C.sub.2 F).sub.n (s) . . . (2)
in the parentheses, s and g represent solid phase and gas phase, respectively. The reaction of Equations (1) and (2) are both exothermic reactions.
However, it is usual that some side reactions accompany either of the reactions of Equations (1) and (2). In the case of the reaction of Equation (1) for example, the following reactions take place as the reaction (1) proceeds: EQU 4(CF).sub.n .fwdarw.3nC*+nCF.sub.4 .uparw. . . . (3) EQU C*+2F.sub.2 .fwdarw.CF.sub.4 .uparw. . . . (4)
wherein C* represents activated carbon.
The reaction of Equation (4) generates particularly large amount of heat of reaction since the heat of formation .DELTA.H of CF.sub.4 by this reaction is as large as -46.7 Kcal/mole and, therefore, causes the temperature of the reaction system to rise significantly. Then the reaction (3) is further promoted with resultant augmentation of the reaction (4), and finally there occurs explodingly rapid and violent decomposition of the entire graphite fluorides in the reaction system. Besides the problem of these side reactions, sometimes depending on the properties of the carbon material the reaction of Equation (1) does not proceed smoothly, and a different reaction represented by the following equation takes place instead. EQU C+2F.sub.2 .fwdarw.CF.sub.4 .uparw. . . . (5)
This reaction too is significantly exothermic and, therefore, becomes a cause of accumulation of heat in the reaction system.
The result of the aforementioned exploding decomposition of the fluorinated carbon is not always limited to the loss of the entire product of the process: sometimes the reaction vessel is seriously damaged by the exploding decomposition. Therefore, in the industrial preparation of a graphite fluoride by reaction between solid carbon such as powdery or granular graphite and fluorine gas, it becomes a matter of important concern to prevent local accumulation of heat generated by the above described exothermic reactions in the solid phase of the reaction system.
Conventional methods for the preparation of graphite fluorides include a batch process, wherein fluorine gas is passed or circulated through a reactor in which a carbon material is placed, and a continuous process wherein both fluorine gas and a powdery or granular carbon material are continuously introduced into a suitably designed reactor such as a rotary kiln. In either process a rotating or vibrating force is exerted on the carbon material under reaction in order to dissipate the heat of reaction from the solid phase of the reaction system and also to realize efficient contact of fluorine gas with the powdery or granular carbon material. However, such agitation of the carbon material cannot be taken as fully effective since the conventional methods have often suffered from decomposition of the formed graphite fluoride.